1. Field of the Invention
The present invention relates to a semiconductor MultiQuantum Well (MQW) structure and a semiconductor laser whose active layer has the MQW structure.
2. Description of the Prior Art
Conventionally, Distributed Feedback (DFB) type semiconductor lasers with the MQW structure used for analog optical transmission are required to be superior in modulation distortion characteristic. For example, in the case of 42-channel subcarrier multiple transmission of Cable TeleVision (CATV), the composite second order (CSO) distortion of the laser has to be -60 dBc or less and the composite triple beat (CTB) distortion thereof has to be -65 Dbc or less, which are very severe specifications.
If the semiconductor MQW laser is employed for High Definition TeleVision (HDTV) whose working frequency band may be a 1 GHz band in the near future, it will be required to be smaller in modulation distortion than the case of CATV because of its higher modulation frequency.
From this point of view, conventional semiconductor lasers designed for analog optical transmission, including the MQW-DFB laser, are not sufficient in distortion characteristic for HDTV application.
Additionally, which the trunk line system of ultra-high-speed digital optical transmission in the near future, a transmission speed of about 10 Gb/s will be required. However, no semiconductor lasers applicable for such application has been realized.